The field of the invention is related to the applications of electronics interconnect with Land or Ball Grid Array (L/BGA) socket and the subsystem assembly.
Land or Ball Grid Array sockets have been used to interconnect high pin count integrated circuits (IC) packages for many years. There are varieties of these sockets available in applications. The terminals of stamped metal are one of the types widely used for these sockets in previous inventions.
As the nanotechnology advances in semiconductor processing, very low K dielectric materials with very low mechanical strength are being used in IC semiconductors to dramatically enhance the electrical performances. The pin count, package size and power of IC packages increase as the IC density increases. Therefore, the requirements for L/BGA socket interconnect become more challenging. The essential requirements for L/BGA socket interconnect are the capability of large travel in Z direction to accommodate the tolerances contributed by the printed circuit board (PCB), package co-planarity and other fixtures, the short electrical path for better electrical performance, and low pressure transferred to semiconductor due to the restriction of low mechanical strength of the dielectric materials used in IC semiconductor.
To solve the mechanical and thermal problems for high pin count and high powered L/BGA electronics packages, the subsystem assembly with L/BGA sockets is very critical. The bolster plate of bow shape is used in the conventional set-up for LGA socket so that the pressure over the LGA socket can be more evenly distributed. An alternative approach to the same propose was invented for LGA multichip modules by IBM (U.S. Pat. Nos. 6,449,155 and 6,475,011) such that the contact force applied to the center of the socket through PCB by a screw at the center from bottom side. To make LGA subassembly simpler, a fixture with a lever was developed for LGA subsystem assembly in the invention (U.S. Pat. No. 6,485,320). In order to share the contact pressure from semiconductor to the package substrate, or to make the subassembly for lidless flip chip package for better heat dissipation, some designs of a cover used on top of the package substrate were innovated, for examples, U.S. Pat. No. 6,545,879 and U.S. Pat. No. 6,626,683. However, the concept is seldom used in application because the tolerances of all components are difficult to control as well as the amount of the force.